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an elevated serum creatinine. This is most commonly associated with renal failure, both acute and chronic. An elevation in the serum creatinine is also seen with ingestion of meat, muscle necrosis, hypovolemia, and secondary to the use of certain medications. Oral sodium phophate bowel preparations may lead to acute phosphate nephropathy especially in elderly or female patients and in hypertensives on ACE inhibitors or ARB's. The serum creatinine is used to determine the GFR via equations such as the Modification of Diet in Renal Disease or the Chronic Kidney Disease Epidemiology Study equations. The calculated GFR is preferred for estimating or following renal disease as the creatinine may give a false sense of security in that small increases in the serum creatinine represent large decreases in the GFR. The serum creatinine may be used to estimate the glomerular filtration rate via the following Cockcroft-Gault equation as follows:

However, most labs now provide a calculated glomerular filtration rate via the Modification of Diet in Renal Disease equation. The normal GFR is as follows:

Males: 97-137 ml/min/1.73m2

Females: 88-128 ml/min/1.73m2 

The various stages of renal impairment are classified based on the degree of reduction in the GFR. A decline in the above values is associated with the normal aging process. A level persistently below 60 mL/min is abnormal. Therefore, stages I and II are only abnormal when patients have a single kidney or have both kidneys but suffer an underlying renal disease or structural abnormality. Early diabetic nephropathy may be associated with a slight rise in the GFR, but can be diagnosed by the presence of microalbuminuria. The following values show the relationship between the degree of renal impairment with the different levels of decreasing GFR:

                     GFR                                                                       STAGE OF RENAL IMPAIRMENT

                     >80                                                                                       STAGE I

                   60-80                                                                                     STAGE II

                   30-60                                                                                     STAGE III

                  15-30                                                                                      STAGE IV

                   <15                                                                                        STAGE V